The forests of the Amazon basin in Brazil have a large impact on global carbon cycling and climate, they harbor a large fraction of the world’s biodiversity, and provide substantial additional ecosystem services to humankind. Future climate change may be particularly severe in the Amazon region, compromising the provision of those services. However, the effect of the increasing concentration of CO2 in the atmosphere on fertilization could buffer the Amazon forest against the deleterious effects of climate change and favor the long-term permanence of the forest. The AmazonFACE (free-air CO2enrichment) experiment is designed to answer the overarching question: “How will rising atmospheric CO2 affect the resilience of the Amazon forest, the biodiversity it harbors, and the ecosystem services it provides?” Led by Brazil’s Instituto Nacional de Pesquisas da Amazônia, an international team of scientists is implementing this experiment of unprecedented size and scope in the magnificent old-growth forest north of Manaus. Pretreatment characterization of the site has already produced a wealth of ecological information.